1. Field of the Invention
The invention relates to an internal combustion engine cooling system of.
2. Description of the Related Art
In an internal combustion engine (hereinafter, also referred to as an engine) installed in a vehicle or the like, it is important to warm up the engine as quickly as possible after the engine is started to improve fuel economy and reduce exhaust emissions.
Conventionally, to quickly warm-up a water-cooled engine, a cooling system stores part of the coolant that has been warmed during the operation of an internal combustion engine and keeps the stored coolant warm. The warm coolant may be stored in a thermal storage tank and used to preheat (pre-warm) the engine before the next engine start (see Japanese Patent Application Publication No. JP-A-2003-184553 and Japanese Patent Application Publication No. JP-A-2005-146950, for example).
FIG. 8 shows one example of a conventional cooling system that preheats an engine.
The cooling system shown in FIG. 8 includes a cooling circuit 301 for cooling a cylinder block 201a and a cylinder head 201b of an engine 201 using coolant; a heater circuit 302 for heating the passenger compartment and some components and devices using coolant that has absorbed heat from the engine (hereinafter “warm coolant”); and a thermal storage circuit 303 for storing the warm coolant until the next engine start.
The cooling circuit 301 includes a mechanical water pump (W/P) 202 driven by the engine 201; a radiator 203 that cools the coolant; and a thermostat 204 that adjusts the flow rate of the coolant flowing into the engine 201 after flowing through the radiator 203. The thermostat 204 adjusts, by changing the opening amount of the valve, the flow rate of the coolant that flows in the cooling circuit 301 while passing through the radiator 203 and the flow rate of the coolant that flows in the cooling circuit 301 without flowing through the radiator 203. The heater circuit 302 is provided with a heater core 205.
The thermal storage circuit 303 is provided with a thermal storage tank 207 that stores warm coolant that has flown into the thermal storage circuit 303, and an electrically driven water pump (W/P) 208. The discharge port of the electrically driven water pump 208 is connected to the thermal storage tank 207.
The cooling system is provided with a three-way valve 206 that selectively connects and disconnects the three circuits, i.e., the cooling circuit 301, the heater circuit 302, and the thermal storage circuit 303. The three-way valve 206 has three ports. A first port P1 is connected to the inlet port of the mechanical water pump 202, a second port P2 to the heater core 205, and a third port P3 to the inlet port of the electrically driven water pump 208.
In the above-described cooling system, when preheating the engine before starting it, the electrically driven water pump 208 is driven with the first port P1 and the third port P3 of the three-way valve 206 open and the second port P2 closed, to supply the warm coolant from the thermal storage tank 207 to the cylinder block 201a and the cylinder head 201b of the engine 1.
Next, while the engine 201 is being warmed up (i.e., while the engine is operating at a low temperature), the ports P1 to P3 of the three-way valve 206 are all closed, so that coolant is circulated to the cylinder block 201a and the cylinder head 201b of the engine 201 through the cooling circuit 301 by the mechanical water pump 202. Further, it is possible to supply the warm coolant to the heater core 205 by opening the first port P1 and the second port P2 of the three-way valve 206 during the operation of the engine 1.
Then, by opening the first port P1 and the third port P3 of the three-way valve 206 while the engine 201 is operating after it has been warmed-up, a part of the warm coolant in the cylinder block 201a of the engine 201 is collected and stored in the thermal storage tank 207. The stored warm coolant is utilized to preheat the engine before the next engine start.
Further, in the case of a system as shown in FIG. 8 in which a three-way valve is used, a positioning sensor such as a potentiometer needs to be provided along with the three-way valve, therefore the production cost is high. Also, in a cooling system including a three-way valve, it is necessary to control the switching of the three-way valve based on particular conditions of the engine operation such as the engine being not operating (before engine start), the engine being presently warmed up, and the warming-up of the engine having been completed, which requires a complicated control system.